Original images include both characters and halftone images. Therefore, it is necessary to prevent moiré generation while ensuring character sharpness. For this purpose, in a conventional image processor, region discrimination is performed to separate the original image into a character edge region and a continuous tone region, and by switching the tone reproduction method between the regions, moiré generation is reduced while character sharpness is ensured. To reduce moiré generation, smoothing on the continuous tone region is widely performed.
However, with the conventional image processor, as shown in FIG. 20, noises are sometimes caused around the character edge region due to smoothing in a reproduced image of an original image (see FIG. 15). This is because the size of the filter for region discrimination is smaller than that of the filter for smoothing. That is, smoothing is performed on white pixels in the continuous tone region existing outside the character edge region. However, when the region determined to be the character edge region by region discrimination is smaller than the size of the filter for smoothing, the filter for smoothing may include some of the characters. When black pixels of characters are included in the filter for smoothing, pixels that should be white pixels have a certain degree of density and produce noises. These noises become more noticeable when dithering or screening is performed. As described above, the conventional image processor causes degradation in reproduced image quality.